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Effect of Presoaking on Extraction of Hemicellulosic Sugars and Flavonoids from Switchgrass (Panicum virgatum) Leaves and Stems

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 54(5): 1953-1957. (doi: 10.13031/2013.39817) @2011
Authors:   E. M. Martin, S. L. Cousins, S. R. Talley, C. P. West, E. C. Clausen, D. J. Carrier
Keywords:   Dilute acid pretreatment, Ethanol, Flavonoid, Switchgrass

In order to establish the baseline quantities of key fermentable sugars, switchgrass (Panicum virgatum L., var. Alamo) stems and leaves were pretreated with dilute acid, and the release of sugars was compared to that reported in the U.S. DOE biomass feedstock composition and property database. Switchgrass was planted in the spring of 2008 and harvested in the spring of 2009. The feedstock was separated into leaves and stems and ground to particle sizes of 0.34 and 0.37 mm, respectively. Dilute acid pretreatment of the material (130C in 0.98% H2SO4 for 25 min) yielded xylose recoveries of 76% and 61% for leaves and stems, respectively. Recoveries were calculated by dividing the recovered sugar by the values reported in the DOE feedstock database. Coupling a 2 h 85C hot water presoaking step to the 25 min 130C in 0.98% H2SO4 pretreatment increased the xylose recovery by 23% and 5% for leaves and stems, respectively. These results demonstrate that a presoaking step increases the sugar release without escalating the severity of the pretreatment. Moreover, the 85C presoaking water contained the flavonoid quercetin, which is a documented antioxidant. The presoaking water from leaves and stems displayed yields of 0.14 and 0.12 mg of quercetin per g of dry switchgrass, respectively. Thus, the presoaking step not only increases monosacchride recovery, but provides a slipstream that could be processed into a value-added revenue-generating stream for the biorefinery.

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